1. Field of the Invention
The present invention relates to an image reading device constructed such that light from a light source is emitted via a contact glass to a document surface of a document placed on the contact glass and a resulting reflected light is inputted to a specified image sensor to read an image.
2. Description of the Related Art
There has been conventionally known an image reading device as disclosed in Japanese Unexamined Patent Publication No. H05-207239. This image reading device is constructed such that a document is placed on a contact glass (referred to as a platen glass in this publication), a document surface of this document is scanned with light from a light source via the contact glass, and this scanning light is inputted to a CCD image sensor to read this image information by converting it into a digital electrical signal. A tubular light source such as a xenon lamp or a cathode-ray lamp is employed as the light source as can be seen in FIG. 1 of this publication. A document mat (referred to as a platen cover in this publication) openable and closable relative to the contact glass for pressing a document is also provided, wherein the document is placed on the contact glass with the document mat opened and, thereafter, an image reading operation is performed by moving the light source with the document mat closed.
In such an image reading device, when the document is placed on the contact glass with the document mat opened and the document is successively closed to press the document, the tubular light source is turned on in synchronism with the document mat closing operation, and the light from this tubular light source reflected by the document is inputted to the CCD image sensor, whereby the CCD image sensor detects the size of the document.
However, the image reading device of the above prior art has a problem that the light emitted from the tubular light source comes into an operator's eyes and is too bright since the tubular light source is turned on every time the document mat is closed. Since the tubular light source is turned on in synchronism with the document mat closing operation, it is, after all, turned on twice for one document reading operation when the document mat is closed after the document is placed on the contact glass and when the document mat is closed after the document is removed from the contact glass following the end of the image reading operation. This considerably influences the operator's eyes (i.e. the operator has to be dazzled twice for one image reading operation).